“its a slam-dunk that courts would say that natural born NOW means born to a US citizen anywhere. “
It depends if they rule on original intent or living document standards.
I think it would be very difficult to solidly establish original intent in this case as there is no real precedent.
And then there is the fact of changes in social structure via the law since then. Original intent could call for only the father being qualified to pass on citizenship for instance (”both parents” is an absurd requirement, even for “original intent”. That was never the custom.). These days it would be absurd to deny the mother the ability to pass on citizenship also.
The whole business is highly unsettled it seems.